The present invention relates to a cleaning device and an image forming apparatus. More specifically, the present invention is preferably applied to cleaning devices provided in image forming apparatuses such as laser printers, copying machines, facsimile devices and multi-function machines of these apparatuses.
An image forming apparatus is provided with a cleaning device for collecting toner remaining on the surface of a photoconductor (e.g., photoconductor drum or photoconductor belt) or an intermediate transfer member (e.g., intermediate transfer belt or intermediate transfer drum) as image bearing bodies after transfer of a toner image. The toner remaining on the surface of the image bearing bodies after transfer is partially charged to a reverse polarity, thus being nonuniform in electric charge distribution. In order to effectively collect such residual toner, various cleaning devices have been proposed .
With reference to FIG. 29, a cleaning device disclosed in Japanese utility model application laid-open publication No. H04-112274 is provided with a pair of fur brushes 2A and 2B disposed so as to be contact with the surface of a photoconductor 1. Bias voltages with polarities opposite to each other are applied to each of the fur brushes 2A, 2B by individual power supplies 3A, 3B. The residual toner with a normal charge polarity (negative polarity) is collected by the fur brush 2A to which a positive-polarity voltage is applied by the power supply source 3A. The residual toner with a reverse polarity (positive polarity) is collected by the fur brush 2B to which a negative-polarity voltage is applied by the power supply 3B.
With reference to FIG. 30, a cleaning device disclosed in Japanese patent application laid-open publication No. H08-50437 is provided with one fur brush 5 disposed so as to be contact with the surface of a photoconductor 4. Bias voltage with a polarity (negative polarity) reverse to a normal charge polarity (positive polarity) of the residual toner is applied to the fur brush 5 via a collection roller 6 having conductivity by a power supply 7A. Upstream from the fur brush 5 in the rotating direction of the photoconductor 4, disposed is a charger 8 connected to a power supply 7B. Before being collected by the fur brush 5, the residual toner is charged or discharged by the charger 8, and their charge polarity is unified. A similar cleaning device is also disclosed in Japanese Patent No. 2954812.
However, the conventional cleaning device requires a plurality of power supplies. For details, in the case of the cleaning device in FIG. 29, two fur brushes 2A, 2B each require one power supply and so the total two power supplies 3A, 3B are necessary. Similarly, in the cleaning device in FIG. 30, the fur brush 5 and the charger 8 each require one power supply and so the total two power supplies 7A, 7B are necessary. This increases size of the cleaning device and costs.
A charge amount of toner remaining on the surface of the image bearing body varies depending on various conditions such as a current flowing to a transfer portion. As in the case of the cleaning device in FIG. 30, if the charger 8 for the discharging purpose is provided before the fur brush 5 as a cleaning member, the charge polarity and the charge amount of the toner having reached the fur brush 5 can be unified. However, since two power supplies are necessary as described before, the cleaning device grows in size. In the case of the cleaning device without a mechanism for discharge such as the charger 8, a voltage to be applied to the cleaning member needs to be set high for securely collecting toner particles different in charge polarity and charge amount. However, this imposes the following problems. First, an excessive cleaning current flowing to an image bearing body charges the image bearing body and this would cause image failures. Moreover, the excessive cleaning current causes the image bearing body to have a shorter life. Further, if the charge amount of the toner is small, the toner is charged with a polarity reverse to a normal charge polarity due to the excessive cleaning current, which degrades a cleaning capability. Similarly, the amount of the toner remaining on the surface of the image bearing body varies depending on various conditions.
A primary transfer device in an image forming apparatus of intermediate transfer method, which is generally provided with a constant-voltage power supply, transfers a toner image on a photoconductor to an intermediate transfer member by applying a constant voltage with a polarity reverse to a normal charge polarity of the toner image. Accordingly, if a resistance of the intermediate transfer member is decreased by duration, or if a humidity inside the image forming apparatus is high, an excessive current generated in a primary transfer device could flow into the cleaning device via the intermediate transfer member. The excessive current generated in the primary transfer device damages the intermediate transfer member and causes the intermediate transfer member to have a shorter life.